Arthritis affects 50 million U.S. adults (most of whom are aged <65 years) with costs of $128 billion annually, and continues to be the most common cause of disability in the United States. By 2030, an estimated 67 million adults (one in four) are expected to be affected by arthritis. In severe cases, total hip replacements (THR) are accepted as a cost-effective and clinically successful intervention. A well functioning THR should be one that is durable (lasting for the duration of the patient's life) and enables the suffering patient o continue a normal life with minimum side effects on the host body. Currently, the average life span of a THR is estimated at 15 years most likely followed by multiple revision surgeries, particularly in the case of younger patients. One of the major concerns for metal-based hip implants is the loosening and subsequent failure of the femoral stem at the modular junction. The modular junction has been of serious concerns because of the coupled action of mechanical micro-motions (fretting) and the contact of two metals while in a corrosive environment that causes variations in the corrosion kinetics mainly due to galvanic coupling. Numerous surface analysis reports of retrieved metal implants have demonstrated evidence of fretting-corrosion at modular junctions. Previous studies on the fretting-corrosion of modular junctions reported the detrimental role of mechanically assisted corrosion (MAC) which is an unpredictable acceleration in the corrosion rates in association with mechanical wear. Hence, the synergistic approach of tribocorrosion that links tribology and corrosion is necessary to identify the pathways of failure at modular junctions. In this investigation the fundamental mechanisms influencing the tribocorrosion behavior of Ti and CoCrMo alloy in a simulated joint environment will be conducted. This technique will address the interaction between mechanical action, electrochemical degradation, metal ions and wear debris present at the modular junction interface. The objective in this application is to clearly define the potential mechanisms enabling the early failure of hip prostheses at the modular junction. We propose the following specific aims. Aim 1: Identify potential fretting regimes and the influence of pH level and load on the corrosion tendency. Aim 2: Study the electrochemical characteristics of the metal interface and the variability of the corrosion kinetics as a function of pH and load Aim 3: Develop a tribocorrosion synergistic model for Ti and CoCrMo alloys and identify the mechanistic transitions as a function of pH and fretting regime. It is expected that after the completion of ths project the failure mechanisms related to tribocorrosion will be determined and design improvements can be proposed to provide a safer modular junction that will assist the NIAMS mission of long-term solutions for the patients at a critical stage of arthritis. PHS 398/2590 (Rev 06/09) Page Continuation Format Page